The paper aims at finding whether the serum creatine-kinase activity may be considered as a biological state or a trait-marker in major depression. The study performed in 76 patients (males and females) led to the conclusion that significant increases of the enzymic activity as compared with controls are present in depressive and not in euthymic patients. The same significant increase was found when comparing the depressive and euthymic patients (but not in the group of monopolar depressive females). There were no significant differences between the monopolar and the bipolar form of the disease. The data reported by the authors show that serum creatine-kinase is not a trait-marker in primary affective illness, but it may be taken for a state-marker in this disease. However, the enzyme is not a biochemical discriminant for the type of depression.